Soda-lime-silica glass, also referred to as soda-lime glass, is commonly used in the commercial production of hollow and flat glass articles, such as glass containers and windows, and is based on a Na2O—CaO—SiO2 ternary system. Relatively small amounts of other oxides may be added to adjust the properties of the glass for various purposes. For example, aluminum oxide (Al2O3), or alumina, is usually included in commercial soda-lime glass compositions to improve chemical resistance, regulate viscosity, and prevent devitrification of the glass. Commercial soda-lime glass compositions generally comprise, by weight, 70-75% silica (SiO2), 11-15% soda (Na2O), 6-12% lime (CaO), and 0.1-3% alumina (Al2O3).
Glass is commercially produced by melting a mixture of solid glass-forming materials known as a glass batch in a melting tank of a continuous glass furnace to produce a volume of molten glass known as a melt. Glass articles having a non-crystalline amorphous structure are produced from the melt by cooling the molten glass along a temperature profile that is calculated to avoid nucleation and crystal growth within the glass. The unintentional and uncontrolled crystallization or devitrification of soda-lime glass is generally considered to be undesirable because it typically results in the heterogeneous formation of relatively coarse crystals of varying size, which can reduce the transparency and mechanical strength of the glass. Also, devitrification of conventional soda-lime glass compositions is known to produce devitrite (Na2O.3CaO.6SiO2), wollastonite (CaO.SiO2), and/or quartz, cristobalite or tridymite (SiO2) crystals within the glass, which reduces the chemical resistance of the residual glass phase by increasing the Na2O concentration therein.
Glass-ceramic materials, having a homogeneous distribution of fine-grained crystals throughout a residual amorphous phase, may be formed by the controlled crystallization or ceramization of a parent glass. In particular, glass articles may be formed from a parent glass composition and then intentionally transformed into glass-ceramic articles by heat treating the parent glass at a temperature above its glass transition temperature (Tg) for a sufficient amount of time for bulk nucleation to occur within the glass, followed by crystal growth. The resulting glass-ceramic articles may exhibit certain desirable and improved properties over that of the parent glass. For example, glass-ceramic articles may exhibit a higher viscosity vs. temperature profile and a lower coefficient of thermal expansion. In addition, the crystal grains in the glass-ceramic articles may inhibit crack propagation, which may result in increased strength.
A general object of the present disclosure, in accordance with one aspect of the disclosure, is to provide a soda-lime-silica parent glass composition that can be used to produce soda-lime-silica glass-ceramic articles having improved chemical resistance and fracture toughness, as compared to conventional soda-lime-silica glass.
The present disclosure embodies a number of aspects that can be implemented separately from or in combination with each other.
In accordance with one aspect of the disclosure, a body of a soda-lime-silica glass-ceramic container, which defines a shape of the container, comprises a soda-lime-silica glass-ceramic having an amorphous matrix phase and a crystalline phase. An overall chemical composition of the soda-lime-silica glass-ceramic comprises 47-63 mol % SiO2, 15-22 mol % Na2O, and 18-36 mol % CaO. The concentration of sodium in the crystalline phase is greater than the concentration of sodium in the amorphous matrix phase.
In accordance with another aspect of the disclosure, there is provided a method of manufacturing a soda-lime-silica glass-ceramic container in which a glass body is initially formed from a parent glass composition that comprises 47-63 mol % SiO2, 15-22 mol % Na2O, and 18-36 mol % CaO. The glass body is in the shape of a container and is subjected to a thermal treatment to promote bulk in situ crystallization of the glass body such that the glass body is transformed into a glass-ceramic body having an amorphous matrix phase and a crystalline phase homogeneously dispersed throughout the amorphous matrix phase.